1. Field of the Invention
The present invention relates to papermakers fabric. More particularly, the present invention relates to the weave construction of forming fabrics and press felts.
2. Description of the Prior Art
Papermaking machines transform an aqueous slurry of pulp fibers into a continuous paper sheet. The papermaking process starts in a forming section of the papermaking machine where an aqueous pulp slurry is deposited onto forming fabrics having desired characteristics for retaining the pulp fibers while allowing water to pass through the fabric. In the forming section, the pulp fibers are formed into an aqueous paper web. The paper web is then transferred to and carried by press felts through a press section of the papermaking machine where additional water is removed by conveying the paper web through one or more press nips. The paper web is then transferred to and carried through a drying section on dryer fabrics to remove additional water through forced evaporation. The designs of papermakers fabrics used on each section of the papermaking machine vary in accordance with function.
Forming fabrics may possess fine mesh weave to support the paper fibers in the slurry. Additionally, a fine weave avoids paper markings on the forming paper. Forming fabrics should also possess good drainage characteristics to facilitate paper formation during the initial water removal from the slurry. Furthermore, the forming fabric should withstand tensile loads in the machine direction and compressive buckling loads in the cross machine direction.
For press felts, several other characteristics are desired. Press felts should maintain sufficient void volume to allow the efficient transfer of water out of the aqueous paper web as it is conveyed through press nips. The press felts should be designed to withstand the humidity and temperature rigors of the press section. Furthermore, the felts should maintain uniformity over a substantial time period as they are used on the press section. In light of these conditions and factors, it is desired to provide press felts with enhanced stability, low flow resistance, compaction resistance, increased void volume, increased cleanability, and durable pressing uniformity.
Attempts have been made to overcome the problems associated with forming fabrics and press felts. For example, U.S. Pat. No. 4,041,989 (Johansson et al.); U.S. Pat. No. 4,642,261 (Fearnhead); U.S. Pat. No. 4,071,050 (Codonik); and U.S. Pat. No. 4,564,052 (Borel) disclose two-layer fabrics having various weave repeats. While these patents disclose fabrics which perform satisfactorily in many applications, it is desirable to provide a structure for forming fabrics and press felts, having improved paper carrying support while maintaining the overall void volume and open area of the fabric.